Research On Evaluation About Excavation Safety Based On Extension Evaluation Method

As China is speeding up the process of urbanization, large number of high-rise buildings and underground construction projects have brought a lot of excavation works. As a result of excavation, a lot of disasters and accidents have been caused. So the study about security assessment and warning is very important.Extension evaluation method is one of the practical applications of Extenics in the field of engineering. Extenics is based on the matter-element theory and extension set theory. With the help of extension set and matter-element, we can judge thing's degree of belonging to a certain collection by its characteristics' money. And the form of an extension to the (- 8, + 8) value of the correlation function enables precise evaluation, quantitative. This means a new way is proposed to achieve comprehensive and objective evaluation.This paper will be the first to make evaluation by extension evaluation method for excavation safety. Two matter-element models are established by extension theory for the evaluation of excavation works grade and the evaluation of excavation safety grade. In order to determine the index weight, two methods have been proposed here under consideration the characteristics of index that in the two evaluations, which are used for engineering practice and get good results.(1) In the comprehensive evaluation for excavation works grade, three factors' affection to the excavation stability is considered, they are the depth of excavation, the groundwater level and soft soil thickness. The analytic hierarchy process method (AHP) is used to determine index weights. AHP uses the traditional 1 to 9 scaling law method to construct the judgement matrix, which seriously rely on experts' experience and impacted by subjective factor of human. In order to avoid this defect, a method is proposed: construct the judgement matrix by using the orthogonal experimental design methods and Finite Element Analysis, and then use the AHP method for index weights.(2) According to various types of monitoring indicators such as the ground surface subsidence, basement uplift, the level displacement of diaphragm wall, the moment of diaphragm wall, the axial force of supporting and so on, make evaluation of excavation safety grade. In this evaluation, the index weight is calculated by Entropy Law, which determines index weight mainly according to the size of index's fluctuations. The calculation principle of Entropy Law meets the features in that monitoring indicators reflect the stability characteristics of excavation. The evaluation by extension evaluation method and Entropy Law can considers both index's money and its changing rate, which is required in early warning analysis for actual project.As a new method to achieve comprehensive and objective evaluation, Extension evaluation method has broad prospects. The paper used it for evaluation about the safety of excavation, and gave out new methods for identification of the weight of factors. The whole way can also be used as a new way for other questions in engineering.